1. Field of the Invention
The present invention relates to a method and an apparatus for testing subscribers accommodated to an FSN (Fiber Service Node) that is connected through an optical fiber cable to an RT (Remote Terminal) connected through a multiplex transmission line to a central office exchange, to thereby construct an FTTH (Fiber To The Home) or FITL (Fiber In The Loop) system.
2. Description of the Related Art
DLC (Digital Loop Carrier) systems are introduced mainly to accommodate many subscribers lying scattered over a vast region. In such DLC systems, an RT located remotely from a central office exchange accommodates a few hundreds of subscribers through metallic cables, and the RT is connected through a multiplex transmission line to the central office exchange. An optical fiber cable is usually used for providing the multiplex transmission line.
In the FTTH or FITL system, the FSN is installed within or near houses of the subscribers in order to use the optical fiber cable having applicability to future broad band communication and economical merits over the future term instead of the metallic cable between the RT and the subscribers. Use of the optical fiber cable between the RT and the subscriber enables a broad band transmission such as video signal transmission. Since the FSN is installed within or near the houses of the subscribers, the FSN is designed to have a capacity of accommodating dozens of subscribers.
So far as the usual DLC systems are concerned, there have been provided two conventional methods of testing subscribers from an operating system connected to the central office exchange. One method is to lay a metallic cable between the operating system and the RT in order to directly test the subscribers from the operating system through the metallic cable. Another method is to locate a test device at the RT and reserve one of the transmission channels of the multiplex transmission line between the central office exchange and the RT for communicating with the testing device. The testing device receives a message including a test command and an identifier of the tested subscriber through the reserved channel from the operating system and notifies the operating system of the results through the reserved channel.
Supposing that the former or the latter method is applied to the FTTH or FITL system, a metallic cable or a reserved transmission channel must be also provided between the RT and the FSN. Since the FSN accommodates relatively fewer subscribers than that of the RT, it requires a greater expenditure to provide a metallic cable or a reserved channel within the optical fiber cable between the RT and the FSN than between the central office exchange and the RT.